This invention relates to fuel injected internal combustion engines where delivery or air injectors respectively deliver metered quantities of fuel directly into the or each cylinder of the engine by means of compressed gas. In engines comprising such two fluid injection systems, the metered quantities of fuel are delivered into the or each combustion chamber of the engine entrained in the gas, typically air, which is supplied from a pressurized gas source, typically a gas duct or rail.
In most engines, a delay is normally experienced between the initial rotation of the engine and the subsequent firing of the engine. Due to commercial and user considerations, this delay or start-up period is typically desired to be as short as possible under a wide range of conditions. For example, an engine may be employed for operation under ambient and extreme ambient conditions. Efficient engine operation is important no matter the conditions.
In engines having a fuel injection system of the type above described, an important part of achieving a rapid start-up period is the ready availability of compressed gas at an adequate pressure to assure effective fuel delivery as close to start of cranking as possible. However, for cost and other considerations, it is not convenient to provide a relatively large compressed air storage capacity or generation means and, in any event, there is also the risk of loss of pressure due to leakage, particularly when the engine has been inoperative for a period.
Typically, a compressor driven by the engine is provided as the means for supplying compressed gas to a two-fluid fuel injection system as above described. For both reasons of economy and energy efficiency, it is customary to select the compressor capacity to closely match the air consumption rate of the engine during running conditions. Thus, the compressor would typically require a certain period of time to increase the air pressure to a suitable level as required during start-up. That is, the compressor, and thus the engine, must complete a number of cycles before air is available for satisfactory injection of fuel at the required pressure.
The above factors contribute to the lengthening of the period between commencement of the start-up sequence of the engine and the availability of air at the required pressure for injection of fuel. In this regard, the Applicant has developed several methods for minimizing the start-up period in certain engines.
In the Applicant""s U.S. Pat. No. 4,936,279, there is described a method of operating an engine during an engine start-up period. The engine includes a gas supply system for supplying gas to the delivery or air injectors. The gas supply system normally includes a gas supply volume, commonly known as an xe2x80x9cair railxe2x80x9d, from which pressurized gas is supplied to each of the delivery injectors. Compressed gas for the air rail is normally supplied by a compressor driven by the engine. As alluded to hereinbefore, the compressor must however complete a number of cycles after engine start-up before the compressor can provide sufficient compressed gas to pressurize the air rail to within a working pressure range. The gas within the air rail and as supplied to the delivery injectors needs to be at a high enough pressure to enable the delivery injectors to inject a metered quantity of fuel into cylinders supporting a piston typically undergoing a compression stroke and therefore containing gas under a relatively high pressure. The pressure of the gas must also be sufficient to enable satisfactory atomisation and entrainment of the fuel being injected. The method described in this patent involves effecting one or more xe2x80x9cpump-upxe2x80x9d events by delivering pressurized gas from respective cylinders of the engine into the gas supply system during the engine start-up period by opening the delivery injector nozzle for each cylinder undergoing a compression stroke of the piston located therein. This results in a progressive increase in the pressure within the gas supply system until the pressure is within the required working pressure range at which time the delivery injectors can begin delivering fuel.
It is further known from the Applicant""s subsequent PCT Patent Application No. PCT/AU97/00438 filed on Jul. 10, 1997 that the delivery injector nozzle 10 may be opened and closed at successively closer timings to the top dead centre (TDC) position of a piston reciprocating in a cylinder of the engine over a sequence of pump-up events to shorten the start-up period of the engine. This patent application also discusses holding the delivery injector nozzle open for a certain period after the engine has commenced firing to continue pressurising the gas supply system prior to the main source of compressed gas being able to adequately pressurize the gas supply system.
It has however been found that the period required to pressurize the air rail to within the working pressure range during start-up of the engine can still be too long for certain engine applications. For example, in cord or pull start engines as typically used in snowmobiles, small outboard engines and lawn-mowers, the start-up period needs to be relatively short, such that start-up can be achieved within the period prior to full extension of the cord. Because the above methods require a sufficient period of time for the engine to determine its angular position and to subsequently pressurize the air rail by suitable means, these methods may therefore not be applicable for certain cord or pull start engines. More generally, the ever increasing requirement for shorter start-up periods may result in these methods not being able to provide for start-up periods below a certain point.
It is therefore an object of the present invention to provide a method of fuel delivery for a two-fluid fuel injection system wherein the gas provided to enable delivery of a metered quantity of fuel into a cylinder of the engine is derived directly from a different cylinder of the engine.
It is a further preferred object of the present invention to provide a method for enabling the reduction of the duration of the start-up period for an engine incorporating a two-fluid fuel injection system.
With this in mind, the present invention provides in one aspect a method of operating an internal combustion engine, the engine having a plurality of cylinders each respectively supporting a piston therein, a fuel injection system including a plurality of selectively operable delivery injector nozzles, and a gas supply system for supplying gas to the delivery injector nozzles, each delivery injector nozzle arranged to respectively deliver fuel by way of said gas directly into a said engine cylinder, the method including opening the delivery injector nozzles of a first said cylinder and a second said cylinder such that gas within the first said cylinder is transferred through the delivery injector nozzle thereof and into the gas supply system resulting in gas being supplied to the delivery injector nozzle of the second said cylinder to thereby effect the delivery of fuel by way of the gas to the second said cylinder, wherein each second said cylinder into which fuel is delivered is operated to effect combustion of said delivered fuel for each cylinder cycle.
The method according to the present invention may be used during start-up of the engine to facilitate the reduction of the start-up time for the engine. It is however also possible for this method to be used when the engine is operating under alternative conditions. For example, the method could be used to operate the engine under a xe2x80x9climp-homexe2x80x9d mode if an air compressor supplying compressed gas to the fuel injection system fails resulting in a loss of pressure within an air rail of the fuel injection system.
The method may be implemented so as to not effect the normal start-up firing sequence of the cylinders, and each delivery injector nozzle and associated cylinder may be operated to effect combustion of a said delivered fuel in the normal manner. That is, the method may be implemented such that each cylinder remains operational to effect combustion in the normal manner. Hence, there is no requirement to cease fuelling to any engine cylinders (ie: to shut them down) or to ship the fuelling event on any cylinder whilst the method of the present invention is being used.
Preferably, the timing of opening and the open period of the delivery injector nozzle of the first said cylinder may be selected so as to provide for a maximum possible pressure to be captured or transferred into the gas supply system from the first said cylinder. This gas pressure may then be used to effect delivery of fuel by way of the gas to the second said cylinder. Typically, some of this gas pressure may remain in the gas supply system after the fuel has been delivered to the second said cylinder such that he pressure in the gas supply system may eventually be increased to a pre-determined level. As cylinder pressure is directly related to crank angle, the opening and closing events for the delivery injector nozzle of the first said cylinder may preferably be controlled with respect to crank angle. Typical timings for any engine configuration for the opening and closing events for the delivery injector nozzle of the first said cylinder are between 90xc2x0 BTDC and 10xc2x0 ATDC. Preferably, the timing of opening of the delivery injector nozzle of the second said cylinder is selected so as to provide for a maximum possible differential pressure between the pressure within the gas supply system and the pressure within the second said cylinder. This ensures that the fuel may be satisfactorily delivered into the second said cylinder by way of gas.
Preferably, the delivery injector nozzle of the first said cylinder is conveniently opened when the gas pressure therein has commenced or is increasing in magnitude. Preferably, the delivery injector nozzle of the first said cylinder is opened while said piston supported therein has initiated or is undergoing a compression stroke.
Preferably, the delivery injector nozzle of the second said cylinder is opened at a point where the gas pressure in said cylinder is lower than the gas pressure in the gas supply system. Conveniently, the delivery injector nozzle of the second said cylinder is opened shortly before or once said piston supported therein has reached the bottom dead centre (BDC) position of its travel. That is, the delivery injector nozzle of the second said cylinder is conveniently opened when the gas pressure therein is at or near its lowest point. In this way, it is ensured that some or all of the gas that has been transferred into the gas supply system from the first said cylinder will subsequently be transferred from the gas supply system into the second said cylinder when the delivery injector nozzle therefore is opened at the same time. Hence, injection may typically occur early in the cylinder cycle of the second said cylinder such that it does not take place against a rising cylinder pressure.
Conveniently, the nozzle of the second said cylinder is opened when said piston supported therein is about to or has just completed an expansion or power stroke. With particular regard to a four-stroke cycle engine, the injector nozzle of the second said cylinder may also or alternatively be opened when said piston supported therein is about to or has just completed an intake or induction stroke. As far as normal engine running, the opening duration of the delivery injector nozzle of the second said cylinder is only a time related dependency. However, the start of the fuel delivery event into the second said cylinder may preferably be phased to crank angle so as to provide for a maximum differential gas pressure across the delivery injector nozzle of the second said cylinder. In this regard, in order to achieve such a maximum differential pressure, the timing of opening of the delivery injector nozzle of the second said cylinder is selected such that the associated gas capture/transfer event on the first said cylinder has been at least substantially or fully completed (ie: ensuring the maximum possible gas pressure has been transferred into the gas supply system). However, the timing of opening of the delivery injector nozzle of the second said cylinder cycle such that the pressure within the second said cylinder has not substantially increased.
Accordingly, the fuel delivery event for the second said cylinder is preferably a duration controlled event that commenced at a defined crank angle. Typical timings of the start angle for the fuel delivery event on a 3 cylinder 2-stroke engine may be between 110-120xc2x0 BTDC whilst on a 4 cylinder 4-stroke engine may be between 170-180xc2x0 BTDC. A typical duration for the opening period of the delivery injector nozzle of the second said cylinder for either engine configuration may be 6 ms.
As noted above, the method of operating an internal combustion engine according to the present invention may be effected during a start-up period of the engine. That is, the method may be effected until the main source of compressed gas is able to adequately pressurize the gas supply system for satisfactory fuel delivery to the engine. Alternatively, the method of the present invention may be effected in combination with one or more of the Applicants"" prior known methods during the start-up period or even after that period.
For example, as alluded to hereinbefore, the opening time and/or period of the injector nozzle of the first said cylinder may be such as to enable gas transfer to effect fuel delivery into the second said cylinder (ie: without the need to bring the pressure in the gas supply system up to a predetermined level over a number of cylinder cycles) as well as to provide some pressurisation of the gas supply system or volume (ie: to a higher level). The opening and closing times of the injector nozzle of the first said cylinder over successive openings thereof may also be arranged to progressively increase the gas pressure in the gas supply system as well as to continue to effect gas transfer to enable fuel delivery into the second said cylinder. That is, for an optimized rate of rise of the pressure in the gas supply system, the crank angle timing for successive gas capture/transfer events may be sequenced such that crank angle opening and closing timings get closer to the TDC position of the first said cylinder as the pressure within the gas supply system rises. This will avoid any back flow of pressure from the gas supply system into the first said cylinder.
Further, pump-up events may continue to occur even after combustion is taking place in a cylinder in the manner as discussed in the Applicant""s PCT Patent Application No. PCT/AU97/00438, the contents of which are included herein by reference.
Conveniently, the gas supply system supplies gas to the delivery injector to effect the delivery of an air/fuel mixture to the engine.
In the case of engines having more than two cylinders, the method may be conducted sequentially over respective pairs of cylinders. It should however be noted that this method does not necessarily limit the method such that successive cylinder pairs must be used in the method. It is possible that one cylinder pair may be bypassed in the sequential event such that there is no gas transfer between that cylinder pair.
Preferably, the opening of the delivery injector nozzles of the first said cylinder and the second said cylinder may be overlapped over a predetermined period. In this way, gas which is transferred into the gas supply system from the first said cylinder effectively results in gas being immediately supplied to the second said cylinder through the delivery injector nozzle thereof to thereby effect the delivery of fuel thereto.
In such a scenario, the delivery injector nozzle of the second said cylinder may conveniently be opened at a point where the gas pressure in said cylinder is lower than the gas pressure in the first said cylinder. It has been found that by overlapping the opening of the injector nozzles of the two noted cylinders, that the volume and pressure of the transferred or displaced gas is sufficient to enable the satisfactory delivery of fuel from the injector nozzle of the second cylinder.
It is to be noted that a metered quantity of fuel will typically be wholly or partly delivered to the delivery injector nozzle of the second said cylinder prior to the transferred gas passing therethrough. Further, in certain circumstances, the metered quantity of fuel will be delivered to the delivery injector nozzle once the transferred or displaced gas has commenced being delivered thereby.
Unlike previous systems, there is no requirement to pressurize the gas supply system over a number of cylinder cycles to a predetermined level before fuel delivery is effected. Accordingly, this results in a significantly shorter start-up period for the engine.
Preferably, the period of opening of the two injector nozzles may be at least substantially identical.. For example, in regard to a three cylinder two-stroke engine, the injector nozzle of the first cylinder may be opened about the TDC point, for example between 90 degrees before TDC to 10 degrees after TDC, while the injector nozzle of the second cylinder may be opened about the BDC point, for example between 210 degrees before TDC to 110 degrees before TDC. The opening and closing times for the injector nozzles may be scheduled in the crank angle domain, time domain, or both, in accordance with known practice.
It is preferable that the delivery of the metered quantity of fuel, particularly during the start-up period, occurs before any significant pressure rise in the second said cylinder and so the inlet and/or exhaust ports of the second cylinder may be open at least during the initial portion of the period of opening of the injector nozzle thereof. That is, the inlet and/or exhaust ports of the second cylinder may be open for the duration or at least part of the fuel injection event within the second cylinder. This ensures that the pressure within the second cylinder remains relatively low during the gas transfer/displacement event to thereby facilitate the injection of the air and fuel mixture into the cylinder.
The gas supply system may include a gas supply volume, typically an air rail, a compressor for supplying compressed gas to the gas supply volume and a communication means between the gas supply volume and the compressor. The gas supply volume may include an isolating means, for example a one-way valve, as is described in the Applicant""s PCT Patent Application No. PCT/AU97/00438, the contents of which are incorporated herein by reference. In this way, the gas supply volume may be isolated from the compressor and preferably also the communication means, at least during the start-up period of the engine. This ensures that gas delivered from a first said injector nozzle is transferred into the gas supply volume and that gas is subsequently delivered therefrom to the next injector nozzle without any of the gas within the gas supply volume entering the volume provided by the communication means and by the compressor. That is, the overall volume of the gas supply system during start-up is reduced which hence increases the gas flow rate from the gas supply system to the injector nozzle of the second cylinder.
According to another aspect of the present invention, there is provided an internal combustion engine having a plurality of cylinders each respectively supporting a piston therein, a fuel injection system including a plurality of selectively operable delivery injector nozzles, and a gas supply system for supplying gas to the delivery injector nozzles, each delivery injector nozzle arranged to respectively deliver fuel by way of said gas directly into a said engine cylinder, said engine including control means for controlling the engine so as to open the delivery injector nozzles of a first said cylinder and of a second said cylinder such that gas within the first said cylinder is transferred through the delivery injector nozzle thereof and into the gas supply system resulting in gas being supplied to the delivery injector nozzle of the second said cylinder to thereby effect the delivery of fuel by way of the gas to the second said cylinder, wherein each second said cylinder into which fuel is delivered is operated to effect combustion of said delivered fuel for each cylinder cycle.
Preferably the control means for controlling the engine does so by selecting the timing of opening and the open period of the first said cylinder so as to provide for a maximum possible pressure to captured or transferred into the gas supply system from the first said cylinder. Conveniently, some of this pressure will be retained in the gas supply system after the fuel has been delivered to the second said cylinder such that the pressure in the gas supply system may eventually be increased to a pre-determined level.
Preferably, the control means controls the timing of opening and the open period of the delivery injector nozzle of the second said cylinder so as to provide for a maximum possible differential pressure between the pressure within the gas supply system and the pressure within the second said cylinder.
Preferably, the control means controls the delivery injector nozzle of the first said cylinder such that it opens whilst said piston supported therein has initiated or is undergoing a compression stroke. Preferably, the control means controls the delivery injector nozzle of the second said cylinder such that it opens at a point where the gas pressure in said cylinder is lower than the gas pressure in the gas supply system. In particular, the control means may open the delivery injector nozzle of the first cylinder about the TDC point, while the control means may open the delivery injector nozzle of the second cylinder about the BDC point. Preferably, the control means for controlling the engine does so by overlapping the opening of the delivery injector nozzle of the first said cylinder and the opening of the delivery injector nozzle of the second said cylinder.
Preferably, the control means controls the engine during a start-up period thereof.
The gas supply system may include a gas supply volume, typically an air rail, a compressor for supplying compressed gas to the gas supply volume and a communication means between the gas supply volume and the compressor.
An isolating means may be provided between the gas supply volume and the compressor for isolating the compressor and preferably also the communication means from the gas supply volume, at least during the start-up period of the engine. The provision of such an isolating means hence allows for rapid pressurisation of the gas supply volume thereby reducing the start-up period of the engine when one of the earlier noted start-up methods is used. The isolating means may include a one-way valve means located between the gas supply volume and the compressor. The communication means between the gas supply volume and the compressor may include a supply conduit and the valve means may alternatively be located between the supply conduit and the gas supply volume. It is also envisaged that the valve means may be located anywhere along the supply conduit.